As representative apparatuses among microwave heating devices for performing heating processing on objects to be heated through microwaves, there are microwave ovens. A microwave oven is adapted to radiate microwaves generated from microwave supply means to the inside of a metal heating chamber, thereby causing an object to be heated within the heating chamber to be subjected to heating processing through radiated microwaves.
Conventional microwave ovens have employed magnetrons as such microwave supply means. Such a magnetron generates microwaves, which are radiated to the inside of the heating chamber from microwave radiating portions through a waveguide tube. A non-uniform microwave electromagnetic-field distribution (microwave distribution) within the heating chamber presents a problem in that uniform microwave heating of the object cannot be heated.
As means for uniformly heating an object to be heated within a heating chamber, there is a structure adapted to rotate a table for placing the object to be heated on the table for rotating the object to be heated within the heating chamber, a structure adapted to rotate an antenna for radiating microwaves while fixing the object to be heated, or a structure adapted to shift the phase of microwaves from microwave supply means using a phase shifter. Microwave heating devices including these structures have been generally used.
For example, some conventional microwave heating devices have been structured to have a rotatable antenna and an antenna shaft which are placed within a waveguide tube and, further, to drive a magnetron while rotating this antenna through a motor, thereby alleviating the non-uniformity in the microwave distribution within the heating chamber.
Further, Unexamined Japanese Patent Publication No. S 62-64093 (Patent Literature 1) describes a microwave heating device having a different structure. This Patent Literature 1 suggests a microwave heating device which is provided with a rotatable antenna at an upper portion of a magnetron and is adapted to direct air flows from a blower fan to the blades of this antenna for rotating the antenna by the wind power from the blower fan, in order to change the microwave distribution within the heating chamber.
As an example of provision of such a phase shifter, U.S. Pat. No. 4,301,347 (Patent Literature 2) describes a microwave heating device which is adapted to alleviate heating unevenness in an object to be heated through microwave heating and to reduce the cost and the space of feeding portions. This Patent Literature 2 suggests a microwave heating device having a single microwave radiating portion for radiating circularly-polarized waves within a heating chamber.
Patent Literature 1: Unexamined Japanese Patent Publication No. S 62-064093
Patent Literature 2: U.S. Pat. No. 4,301,347